Gas-filled discharge lamp



Aug. 16, 1955 R. D. HANCOCK 2, 15,696

GAS-FILLED DISCHARGE LAMP Filed Aug. 28, 1951 LOW waez FU/VC r HIGH WOQK Fl/IVCf/Q V United States Patent Ofi ice Patented Aug. 16, 1955 GAS-FILLED DISCHARGE LAMP Robert D. Hancock, Compton, Calif., assignor to Northrop Aircraft, Iuc., Hawthorne, Calif., a corporation of California Application August 28, 1951, Serial No. 244,003

2 Claims. (31. 313-210 The present invention relates to cold cathode ionic glow tubes and more particularly to cold cathode glow tubes wherein a plurality of electrodes are used in an envelope filled with a gas at glow discharge pressure, to render visible indication of the condition of an external circuit.

It has been found in the manufacture of glow tubes that if the materials used in making the glowing electrodes to be used in the tube are generally similar in work function to the material used in making the electrode lead wires, the glow surrounding the electrode in an envelope which is filled with a gas at glow discharge will also extend to its respective lead Wire, when the lead wire is exposed to the gas in the envelope. This condition may be highly undesirable in indicator tubes and electronic read-out tubes for example, as is well known in the art.

It has usually been the practice in such cases to provide the lead wires and support wires for the glow electrodes where exposed to the gas in the tube, with a coating of an insulating material to prevent these wires from glowing when the electrodes are energized.

It is an object of the present invention to provide a cold cathode ionic glow tube such that the cathode support wires and lead wire will not require an insulation covering.

Briefly, the present invention provides a cold cathode glow tube wherein the electrodes and their associated lead wires are formed of materials that differ widely in their electronic work function, thereby limiting the glow discharge of the ionic glow tube to the electrodes only.

This invention proposes numerous other objects and features, some of which together with the foregoing, will be set forth in the following description of a preferred embodiment of the invention, and the invention will be more fully understood by reference to the attached drawing of a perspective view of an alternating current type cold cathode ionic glow tube.

Referring to the drawing, an envelope 11 is shown having a pair of glow electrodes 12 positioned therein and connected to a. pair of lead wires 14. The envelope 11 is evacuated and filled with suitable gas or vapor at such pressure that a glow discharge will occur when the electrodes 12 are properly energized with alternating potential. The envelope 11 is thereafter sealed.

If materials employed in forming the electrodes 12 and their lead wires 14 are similar in their electronic work function, the glow surrounding the electrodes 12 may extend to the lead wires which are also exposed to the gas, when the electrode lead wires 14 are energized.

In accordance with the present invention, the electrodes 12 are formed of a material that has a comparatively low work function such as barium, thorium, or tantalum, or compounds thereof. Thoriated tungsten, for example, is satisfactory with a work function of about 2.6 volts. The lead wires 14 are formed of a material that offers a comparatively high work function, such as platinum, for example, with a work function of about 6.27 volts. The work function differential between the electrodes 12 and their lead wires 14 will cause a sufiicient difference in the voltage necessary to establish a glow discharge between the leads 14 and between the electrodes 12. This glow discharge voltage differential is sufiicient that the electrodes 12 may be brought to a glow condition without causing the lead wires 14, or sections thereof, to glow.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise the preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

1. A glow tube consisting of an envelope having a filling of a gas at glow discharge pressure, a pair of cylindrical cold electrodes positioned parallel to each other in said envelope, both said electrodes being identical and made throughout of thoriated tungsten, a lead wire connected to each said electrode and passing through said envelope, said lead wires being exposed at their inner ends to said gas within said envelope, each of said leads being identical and made of platinum, whereby when a suitable source of alternating potential is connected across said lead wires, both said electrodes will glow equally and said inner ends of said lead wires will not glow.

2. In a glow tube having a filling of gas at glow discharge pressure: a plurality of cylindrical cold electrodes supported parallel to each other, at least one of said electrodes being made throughout of thoriated tungsten, and a platinum lead-in wire connected to said one electrode and exposed to the filling of gas, whereby said one electrode can be glowed to the exclusion of a glow on said exposed lead-in wire.

References Cited in the file of this patent UNITED STATES PATENTS 251,544 Edison Dec. 27, 1881 1,965,586 Foulke July 10, 1934 2,003,493 Rentschler June 4, 1935 2,057,522 Henninger Oct. 13, 1936 2,217,448 Muller Oct. 8, 1940 2,460,738 Francis Feb. 1, 1949 2,629,837 Benade et a1 Feb. 24, 1953 

1. A GLOW TUBE CONSISTING OF AN ENVELOPE HAVING A FILLING OF A GAS AT GLOW DISCHARGE PRESSURE, A PAIR OF CYLINDRICAL COLD ELECTRODES POSITIONED PARALLEL TO SAID OTHER IN SAID ENVELOPE, BOTH SAID ELECTRODES BEING INDENTICAL AND MADE THROUGHOUT OF THORIATED TUNGSTEN, A LEAD WIRE CONNECTED TO EACH SAID ELECTRODE AND PASSING THROUGH SAID ENVELOPE, SAID LEAD WIRES BEING EXPOSED AT THEIR INNER ENDS TO SID GAS WITHIN SAID ENVELOPE, EACH OF SAID LEADS BEING IDENTICAL AND MADE OF PLATINUM, WHEREBY WHEN A SUITABLE SOURCE OF ALTERNATING POTENTIALS IS CONNECTED ACROSS SAID LEAD WIRES, BOTH SAID ELECTRODES WILL GLOW EQUALLY AND SAID INNER ENDS OF SAID LEAD WIRES WILL NOT GLOW. 